Field of the Invention
The present invention relates to multi-chassis link aggregation.
Description of the Related Technology
It is desirable to provide redundancy and protection against failure in network nodes which interconnect two networks. Link Aggregation (LAG) was originally designed to operate between two devices having multiple links between them. LAG allows the two devices to treat the multiple links as if they were one link, termed a bundle. This provides improved bandwidth (when more than one link is selected in the bundle) and/or protection against link failure within the bundle (when one or more links are selected in the bundle and others are standby).
LAG does not specifically address the situation where multiple links between more than two devices could be selected to provide interconnection between two networks. For example a device providing connectivity to one network could be multi-homed to two or more devices in another network. This is particularly beneficial when redundancy and failure protection is desired because it can provide protection against device failure and isolation of a device from its connected network in addition to link failure. The operation of multi-chassis link aggregation (MC-LAG) to provide redundancy and failover protection has been proposed to provide 1:N protection; a single node on one side (for example a customer side) has physical connections to several nodes on the other side (for example a provider side).
A first known system provides link aggregation and operation of a relay network comprising four interconnected boundary nodes, two on each side. Each side of the relay network is connected to a single communication node through Link Aggregation. Messages are exchanged between nodes in the relay network using Advanced Protection Switching (APS) format. The boundary nodes operate to select a network path within the relay. To connect the communication node at each end to the correct boundary node selected by the relay network, multi-chassis link aggregation is used between each communication node and its respective boundary group, which is the two nodes of the relay network with connections to the communication node.
A second known system provides a “2×2 attached” interconnected zone which connects two packet networks. The zone includes two nodes on each side with network connections to the two nodes on the other side. On one side a node is designated as the “master” and the other node as the “deputy”. The two nodes on the other side are both designated as “slave” nodes. In operation the master selects which of its interfaces is used for network traffic between the two packet networks. On the other side, the slave nodes follow the master's decision. If the master node fails, the deputy node acts as the substitute for the master node.
Both these systems have limited interoperability with other equipment because all four nodes must operate according to the system. It is complicated to extend the systems to more than four nodes.